The goal of this research is purificatin and characterization of endo-xyloglucan transferase, a novel enzyme capable of catalyzing transfer of a segment of one xyloglucan molecule to another.A new approach was developed for quantification of this new enzyme : Purified xyloglucans with defined molecular weight distributions and their fluorescent derivatives were used as donor and acceptor substrates, respectively, for the enzyme reaction. This new procedure was successfully exploited for the first purification of endo-xyloglucan transferase from apoplast of the Vigna angularis. The enzyme is a glycoprotein with a molecular weight of about 33000 and catalyzes both endo-type splitting of a xyloglucan molecule and linking of a newly generated reducing end of the xyloglucan molecule to the non-reducing terminus of another molecule, thereby mediating molecular grafting between xyloglucans. It exhibits no glycosidase or glycanase activity. The transferase required basic xyloglucan structure, i. e. a beta(1-4)-glucosyl backbone with xylosyl side chains, for both acceptor and donor activity. The enzyme exhibited higher reaction rates when xyloglucans with higher molecular weight were used as donor substrates. This enzyme is the first enzyme identified that mediates the transfer of a high molecular weight segment between polysaccharide molecules to generate chimeric polymers. We conclude that endo-xyloglucan tarnsferase functions as a reconstructing enzyme for xyloglucans and is involved in the interweaving or reconstruction of cell wall matrix, which is responsible for chemical creepage that leads to morphological changes in the cell wall.本研究により植物細胞壁マトリックスの構築と再編成に関与する転移酵素の存在とその生理機能が初めて実証されたことになり、植物の細胞成長の分子機構の全容の解明の糸口となるものと思われる。